Exam 14: Genetic Mapping in Eukaryotes

A red,round,true-breeding tomato is bred with a yellow,oval,true-breeding tomato,and the F₁s are testcrossed to a homozygous-recessive tester.This results in the offspring below.Calculate the chi-squared value to test the likelihood of linkage. yellow oval 11 red round 14 yellow round 7 red oval 8

A testcross of trihybrid Drosophila produced the following phenotypes and number of offspring. A table showing phenotype and the number of offspring with each phenotype is below. A plus sign is used for wild-type phenotype; a letter indicates the mutant phenotype for that gene. +++ 669 abc 653 ++c 121 ab+ 139 +b+ 2280 a+c 2215 +bc 3 a++ 2 -Which gene pair is closer together; i.e.there are fewer map units between them?

If an AABB strain is mated with an aabb strain,an AB gamete produced by the resulting F₁ is

A linkage map illustrates the exact physical locations of genes on a chromosome.

What does the chi-square test tell us about the linkage of two genes?

What is the difference in the likelihood of linkage between two genes with a lod score of 2 and two genes with a lod score of 3?

The closer together two genes are on a chromosome,

Why does the recombination frequency often lead to an underestimation of the true map distance between linked genes?

If genes are linked and an F₁ is testcrossed,

X, Y, and Z are linked genes. Based on testcross data, the frequency of recombination between genes X and Y was determined to be 33.1 map units. Between genes X and Z, the distance was 11.8 mu; between genes Y and Z, the distance was 21.3 mu. -What is the order of these three genes on the chromosome?

A testcross of trihybrid Drosophila produced the following phenotypes and number of offspring. A table showing phenotype and the number of offspring with each phenotype is below. A plus sign is used for wild-type phenotype; a letter indicates the mutant phenotype for that gene. +++ 669 abc 653 ++c 121 ab+ 139 +b+ 2280 a+c 2215 +bc 3 a++ 2 -The cross represented by a^+b+c+/abc × abc/abc is

T.H.Morgan and his colleagues found that among the offspring of genetic crosses,parental phenotypic classes were the most frequent,while recombinant classes occurred less frequently.This observation led Morgan to conclude that

Testcrosses may be used to determine if two genes are linked.

A chi-square analysis of linkage between genes k and f produces a P value of 0.99.What is the likelihood that these two genes are linked?

Explain how Curt Stern showed,using evidence from Drosophila,that genetic recombination is associated with the physical exchange of parts between homologous chromosomes.

A coefficient of coincidence of zero is the same as an interference value of zero.

If in calculating the distance between two genes using data from a testcrossed dihybrid you arrive at a genetic distance of 70 map units,there is likely to be something wrong with your calculations,the experimental data,or with the experiment itself.

Genes may show 50% recombination either when the genes are on different chromosomes or when the genes are far apart on the same chromosome.

X, Y, and Z are linked genes. Based on testcross data, the frequency of recombination between genes X and Y was determined to be 33.1 map units. Between genes X and Z, the distance was 11.8 mu; between genes Y and Z, the distance was 21.3 mu. -Of the three pairs of genes,which ones are closest to each other and which ones are farthest apart?